This invention relates to a process for lowering a basement into the ground.
As shown in FIG. 1, in an early process for constructing a basement, fence plates 11 are installed around a previously made excavation to prevent soil from falling thereinto, H-beams 12 are set up to bear against the fence plates, and then floors, walls, etc. are formed in the excavation.
An improved process developed in Italy called "ICOS process" is illustrated in FIGS. 2a to 2d. The process comprises excavating a marginal channel around a region in which a basement will be constructed followed by drilling holes successively in the ground along the channel (FIG. 2a), introducing a soil stabilizing solution into the ground during the hole drilling process (FIG. 2-b), placing a reinforcement frame in each hole (FIG. 2-c), and grouting each hole through tremie pipes (FIG. 2d). This process provides a continuous wall 15 as shown in FIG. 3, around the region in which the basement is to be formed. Excavation is effected in the region surrounded by the continuous wall 15. A first floor 17 of the basement is formed in the excavation and then soil is excavated for forming a second basement floor.
In a caisson process, a frame of a basement is prefabricated on the ground, and then the bottom of the frame is provided with cutting shoes to facilitate the lowering of the basement frame, as shown in FIG. 4a. After constructing the basement frame, the soil below the basement is excavated, as shown in FIG. 4b and is then conveyed away by means of skip buckets. During excavation, the storey above the basement is constructed simultaneously so that sufficient weight is added to force the basement frame downward as shown in FIG. 4c.
When the basement is lowered to a substantial depth, the speed of excavating at the central portion of the excavation is increased to achieve a predetermined depth. Then, piles are constructed from the central portion to the lateral portions as shown in FIG. 4d. After, the basement frame reaches a predetermined depth, concrete is formed on the basement frame. Final construction is shown in FIG. 4e.
The above-described caisson process overcomes many of the drawbacks existing in the conventional processes. However, the caisson process still suffers from several disadvantages. When the properties of the bearing soil are not uniform, the basement frame or the building constructed therein is liable to tilt. Furthermore, if the weight of the building above the basement frame is not sufficient, it may be impossible to force the basement frame down to a desired depth. Moreover, the process of providing cutting shoes at the bottom of the basement frame is difficult, and it is difficult to maintain a proper vertical descent of the basement frame by means of such shoes. The above described process is effective when a building is to be constructed on a bearing strata which is comprised of dense or hard soil. In a case where the bearing strata consists of loose soil, the surrounding soil falls into the region in which the basement will be installed, thereby adversely affecting the bearing capacity of the surrounding soil.